web: rename a category inline with duplicate-name handling

[rghvgrv]

Parent

#196 — PRD: Angular web client for SubVora (parity minus reminders)

What to build

Renaming a user's own category inline, with the duplicate-name conflict handled in place. Renames must also propagate to anything already displaying the old name, since the subscription list groups by category name.

Implementation Steps

1. API method — add rename(id, name) to core/api/categories-api.service.ts (200 with the updated category, 404 for a system default or another user's, 409 for a duplicate).
2. Inline edit — in features/categories/categories.component.ts, make a user category's name editable in place with save and cancel, reusing the same validation as create (required, ≤100).
3. Store method — rename(id, name) in categories.store.ts replaces the item on success; a 409 surfaces "A category with this name already exists." against the field and leaves the item unchanged; a 404 reports "Not found." and reloads the list.
4. Propagate — after a successful rename, refresh the subscriptions list store if it holds data, so its group headings and category cells stop showing the old name.
5. Spec — categories.store.spec.ts additions: rename replaces exactly one item; 409 leaves the list untouched and reports the duplicate message; a successful rename triggers the subscription refresh.

Agent Routing

agent_routing:
  complexity_hint: easy
  required_capability: balanced
  parallel_safe: true
  cost_preference: low
  speed_preference: balanced
  ownership_scope:
    - src/SubVora.Web/src/app/features/categories/**
    - src/SubVora.Web/src/app/core/api/categories-api.service.ts
  verification:
    - cd src/SubVora.Web && npx ng test --no-watch

Technical Context Snapshot

Current stack in scope

• UI: Angular (20+) standalone components with signals and built-in control flow, Angular Material (Material 3) as the only component library, SCSS. Static SPA — no SSR, no service worker.
• State: signal-backed injectable stores, one per domain area, mirroring the MAUI ViewModel split in src/SubVora.Mobile/ViewModels one-to-one. No NgRx.
• API access: hand-written models plus one service per API controller under src/SubVora.Web/src/app/core/api. Enums travel as JSON strings (JsonStringEnumConverter in Program.cs), so TypeScript string-literal unions are exact.
• Backend consumed unchanged: ASP.NET Core net10.0, /api/v1/, JWT bearer in the Authorization header, tokens in JSON bodies (no cookies).
• Tests: Angular CLI unit-test builder (Vitest runner; Karma is deprecated) with HttpTestingController. Stores, interceptors, mappers and utils only — no component-DOM or browser automation.

Dependencies in scope

• Reuse: @angular/*, @angular/material, rxjs, and the utilities already added under src/SubVora.Web/src/app/core. No chart library, no date library, no HTTP wrapper library.
• New dependency additions allowed for this slice: no. If a dependency looks unavoidable, stop and raise it on the issue rather than adding it.

Architecture alignment

• Preserve the repo's load-bearing rules (CLAUDE.md): burn-rate maths is server-side and counts cycles, never days; currency conversion is a read-time projection and stored amounts are never overwritten; nothing advances next_billing_date on a timer; provider matching stays one SQL query; the mobile SQLite cache stays a read-only mirror.
• There is deliberately no shared DTO project. Web models mirror the API's JSON contract by convention — a contract change means editing both sides.
• create-git-issue provides routing hints only and assigns no concrete agent or model.
• run-with-it remains the final runtime routing authority.

Integration touchpoints

• Consumes PUT /api/v1/categories/{id} — 200, 404 (system default or not owned), 409 (duplicate name).
• Subscription DTOs carry categoryName denormalised, so a rename requires refreshing the subscriptions list rather than patching a local string.
• System defaults must not offer a rename affordance at all.

Acceptance criteria

• A user category can be renamed inline; system defaults offer no rename action.
• A duplicate name shows the server message against the field and changes nothing.
• After a rename, the subscriptions screen no longer shows the old name.

Blocked by

• web: categories screen with inline create #222 (slice 26)